The long-standing SDLP assembly member John Dallat has died at the age of 73.
Mr Dallat, who had been diagnosed with cancer last year, had worked as a teacher before being elected to the assembly in 1998 to represent East Londonderry.
He grew up in Kilrea, County Londonderry, and also served for many years on Coleraine Borough Council.
SDLP leader Colum Eastwood said Mr Dallat had "lived and breathed to serve others".
Mr Dallat had undergone cancer treatment while continuing in his role as an assembly member.
'Hand of friendship'
Mr Eastwood said the East Londonderry representative would be remembered for his defence of the public purse and his "famous good humour".
"I know I speak for everyone in the party when I say his good humour and wise advice will be sorely missed," he said.
"John entered public life at a time and in a place when it was difficult to be an SDLP representative.
"I know that, despite his tough exterior, he was often hurt when the hand of friendship he extended across the sectarian divide in the late 1970s and early 1980s on Coleraine Council wasn't always accepted.
"But it never stopped him trying and only strengthened his lifelong resolve to oppose violence and its supporters."
Mr Dallat became Coleraine Borough Council's first nationalist mayor in 2001 until 2002.
He also served as deputy speaker of the NI Assembly from 2007 until 2016.
He retired briefly in May 2016 but when a snap election was called just eight months later, he decided to re-enter political life and regained the East Londonderry seat.
'SDLP to the core'
He is survived by his wife Anne, his three children and eight grandchildren.
"John's family meant everything to him," added Mr Eastwood.
"We're thinking of them at this difficult time and I hope they are comforted by the knowledge that he made an immeasurable difference."
In a statement on behalf of former SDLP leader John Hume, his wife Pat said Mr Dallat was "SDLP to the core".
"During a distinguished political career, he was always on the side of the underdog, defending those who were disadvantaged and standing strong against violence, sectarianism and unfairness in society," the statement added.
First Minister Arlene Foster said her party, the DUP, was deeply saddened to learn of his passing.
"We came from very different political outlooks but he was always to the fore in speaking up for his constituents," added Mrs Foster.
Deputy First Minister Michelle O'Neill said she always found Mr Dallat to be a "pleasant and witty man", and expressed her condolences.
Alliance leader Naomi Long said his death represented a "genuine loss" for Northern Ireland politics, while Ulster Unionist MLA and deputy speaker, Roy Beggs, said he spoke for the whole of the assembly in saying Mr Dallat would be "sorely missed".
The assembly will hold a special sitting next week to allow MLAs to pay tribute to Mr Dallat in the chamber.